NoMethodError: undefined method `value' for #<Nokogiri::XML::Element:0x000000033ad650>

[drh-stanford]

We're seeing an error in production for dor_indexing_app:

NoMethodError: undefined method `value' for #<Nokogiri::XML::Element:0x000000033ad650>

See https://github.com/sul-dlss/dor-rights-auth/blob/v1.2.0/lib/dor/rights_auth.rb#L257

Here were the request parameters from Honeybadger:

{
  "commitWithin" => "10000",
  "controller" => "dor",
  "action" => "reindex",
  "pid" => "druid:bd909yc5623"
}
failure at rights_auth.rb 257 extract_index_terms(...)
[GEM_ROOT]/gems/dor-rights-auth-1.2.0/lib/dor/rights_auth.rb:257:in `extract_index_terms'

The current rightsMetadata datastream is:

<rightsMetadata>
  <access type="discover">
    <machine>
      <world></world>
    </machine>
  </access>
  <access type="read">
    <machine>
      <location rule="no-download">music</location>
    </machine>
  </access>
  <use>
    <human type="useAndReproduction">Property rights reside with the repository. Literary rights reside with the creators of the documents or their heirs. To obtain permission to publish or reproduce, please contact the Stanford Archive of Recorded Sound at [email protected].</human>
  </use>
  <use>
    <human type="creativeCommons"></human>
    <machine type="creativeCommons"></machine>
  </use>
</rightsMetadata>

but it doesn't have a group element. I looked back in the version history and found one with that element:

<rightsMetadata>
  <access type="discover">
    <machine>
      <world></world>
    </machine>
  </access>
  <access type="read">
    <machine>
      <group rule="no-download">music</group>
    </machine>
  </access>
  <use>
    <human type="useAndReproduction">Property rights reside with the repository. Literary rights reside with the creators of the documents or their heirs. To obtain permission to publish or reproduce, please contact the Stanford Archive of Recorded Sound at [email protected].</human>
  </use>
  <use>
    <human type="creativeCommons"></human>
    <machine type="creativeCommons"></machine>
  </use>
</rightsMetadata>